The present invention relates to malodorous gas treatment; more particularly, to a method for the removal of malodorous compounds from atmosphere by use of a catalytic-absorption and oxidation process under a mild condition.
Various malodorous compounds are generated at many industrial plants, sewage collection systems, wastewater treatment facilities, garbage incineration plants and reclaimed landfill sites. Because these malodorous compounds cause air pollution problem, particularly in a closed working space, many efforts have been made to develop an efficient process to remove them.
The removal of the malodorous compounds from atmosphere has been conducted by adsorption, water-absorption, biological treatment and combustion processes. The combustion process may be applied to malodorous compounds present in a large amount and at a high concentration, but it requires a high cost. Further, the adsorption process using an adsorbent provides a significant effect in the treatment of fatty acids, mercaptans, aliphatic or aromatic hydrocarbons and organic chlorinated compounds, but it is less effective in the treatment of major malodorous compounds having low adsorptivity such as hydrogen sulfide, chlorine, formaldehyde and ammonia. Furthermore, the biological treatment with microorganisms has a low efficiency.
On the other hand, the water-absorption process generates a large amount of wastewater, thus requiring an additional treatment process. To deal with such a secondary pollution problem, JP 56-31424 suggests a method for the treatment of malodor, particularly chloric odor, which comprises bringing the malodorous gas into contact with an alkaline cleaning liquid of pH 10 to 13 and then with a cleaning liquid maintained at a pH of 6 to 8 by use of sodium hypochlorite and an acid. This process, however, is not suitably applicable to a variety of other malodorous wastewater streams.
Further, U.S. Pat. No. 5,948,269 issued on Sep. 7, 1999 discloses a process for the removal of dissolved hydrogen sulfide and other malodorous compounds in a liquid or sludge wastewater. This process is characterized by adding an alkaline iron product such as ferrous hydroxide, ferrous carbonate, ferrous bicarbonate, hydrated ferrous oxide and ferric hydroxide. This method still has the problem of an expensive ligand to stabilize Fe ions in solution and generating toxic wastewater containing large amounts of nitrogen and, moreover, and the pH control of the solution is a crucial part of this process, which is a drawback of the system.
The present inventors has attempted to develop a catalytic absorption and catalytic oxidation process effective for the treatment of malodorous gas, and found that specific catalysts can be beneficially used for the treatment of malodorous gas dissolved in wastewater.
It is, therefore, a primary object of the invention to provide a catalytic deodorization process useful for treating malodorous gases.
In accordance with an aspect of the present invention, there is provided a process for treating malodorous gases, which comprises: (a) bringing the malodorous gases into contact with a scrubbing water containing a catalyst to absorb the malodorous components catalytically, and (b) subjecting the resulting solution containing the malodorous compounds to a catalytic oxidation by contacting it with an oxidizing agent in the presence of the catalyst at a temperature ranging from 0 to 100xc2x0 C. under an ambient pressure, the catalyst comprising an active metallic element selected from alkali, alkaline earth and transition metals, and an optional oxide support material.